In the formation of coupled polymers, an alkali metal or alkaline earth metal terminated polymer is treated with a polyfunctional compound containing two or more reactive sites capable of reacting with the carbon-metal bonds of the alkaline earth or alkali metal terminated polymer. Polymers derived from difunctional coupling agents are linear, while coupled polymers derived from coupling agents possessing three or more reactive sites are termed "radial polymers". Coupled polymers, particularly the radial polymers, have been of particular value because of the improvements in Mooney viscosity, processibility, and reduction in cold flow that these polymers exhibit relative to their respective parent uncoupled polymers.
Hydrogenation of polymers to reduce the unsaturation within the polymers improves the polymer resistance to environmental attack, e.g., from oxygen and/or ozone. Effectiveness of hydrogenation, and the value of the resultant hydrogenated polymer, is dependent on the reasonable completeness of the hydrogenation, particularly of the olefinic unsaturation, otherwise significant degrees of remaining olefinic unsaturation provide sites for degradative environmental attack.
Contaminants that impede hydrogenation theoretically can be removed by repeated coagulation, recovery, purification by various means such as molecular sieves, redissolution, and the like, of the polymer. These treatments, however, add expense, and in themselves may introduce contaminants, due to traces of oxygen, moisture and the like, in the solvents used.
At the same time, improvements have been sought with regard to hydrogenation conditions and parameters. For example, minimizing the time of exposure of the polymer to peak hydrogenation temperatures assists in avoiding breakdown of the polymer during hydrogenation, thus maintaining, as far as possible, benefits obtained from the increase in molecular weight, increased Mooney values, obtained through the coupling procedures.